O-alkyl,O-alkyl phosphorochloridothioates are known intermediates for the production of pesticides (see, e.g., U.S. Pat. Nos. 4,127,652 and 4,666,894).
The reaction of thiophosphoryl chloride with an alcohol to produce an O-alkylphosphorodichloridothioate is known. In addition, the reaction of an O-alkylphosphorodichloridothioates with an alcohol to produce an O-alkyl,O-alkyl phosphorochloridothioate is also known. It is also known that these processes can be carried out in the presence of tertiary amines. These two reaction schemes are broadly described in ORGANIC PHOSPHOROUS COMPOUNDS, Volume 7 (1976), pages 500-502 (see also, U.S. Pat. No. 3,790,649). When tertiary amines are used, solid HCI salts of the tertiary amines are formed. These salts typically require the use of significant amounts of solvent in order to allow the salts to be slurried and/or solubilized.
The invention provides an improved process for preparing O-alkyl,O-alkyl phosphorochloridothioates at acceptable reaction rates, purity and yield, without the need to use large amounts of solvent. In the most preferred embodiment, the intermediate product is not isolated.